Laser diode drive circuit and amplifying circuit for optical disc recording and/or reproducing apparatus

ABSTRACT

A laser diode drive circuit for an optical disc recording and/or reproducing apparatus includes a plurality of laser diodes to output laser beams having different wavelengths, a switch circuit for selectively connecting a required laser diode from a plurality of laser diodes, a laser diode drive power supply circuit for driving the laser diode selectively connected by the switch circuit, a photodiode for detecting at least part of laser beams emitted from the laser diode to convert a detected part of laser beams into an electrical signal, a plurality of current-to-voltage conversion amplifiers connected to an output of the photodiode and whose conversion resistance values can be adjusted and having differently designed center conversion resistance values and an automatic power control circuit connected to outputs of the current-to-voltage conversion amplifiers to output a feedback signal to the laser diode drive power supply circuit. An amplifying circuit for such a laser diode drive power supply circuit, an optical disc recording and/or reproducing apparatus including such a laser diode drive circuit and a laser diode drive method for an optical disc recording and/or reproducing apparatus are also provided.

This application is a continuation of U.S. application Ser. No.10/784,745, filed on Feb. 24, 2004 now U.S. Pat. No. 7,035,195, which isa continuation of U.S. application Ser. No. 10/173,246, filed on Jun.18, 2002, now U.S. Pat. No. 6,724,793, and is based upon and claims thebenefits of priority from the prior Japanese Patent Application No.2001-185251, filed on Jun. 19, 2001; all of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a laser diode drive circuitand an amplifying circuit for use in an optical disc recording and/orreproducing apparatus. More particularly, this invention relates to acurrent-to-voltage (I/V) converting circuit for use with a front monitorphotodetector (FPD) and to a laser diode drive circuit using theabove-mentioned current-to-voltage converting circuit.

2. Description of the Related Art

In recent years, a demand for an optical disc drive apparatus called“super disc drive” capable of reading and writing both a compactdisc-recordable/rewritable (CD-R/RW) and a digital versatile disc (ordigital video disc)-recordable/rewritable (DVD-R/RW) has been increasingon the market.

The optical disc drive apparatus of this kind generally uses a powermonitor circuit to detect light intensity of laser beams. This powermonitor circuit includes a monitor diode to receive several percents(this numerical value changes depending upon design of optical system)of laser beams emitted from a laser diode (LD). In that case, when thepower monitor circuit includes only one laser diode LD, a change inquantity of incident light due to a fluctuation of a divergent angle ofthe laser diode LD or due to a fluctuation of a beam splitter is withina range of approximately ±6 dB.

When the change in the quantity of incident light falls within theabove-mentioned range, it is possible to adjust the conversionresistance value of the current-to-voltage converting circuit of thefront monitor photodetector circuit in response to dispersion ofindividual operational amplifiers without sacrificing the performancesuch as an operation band, offset, or the like.

However, let us consider now the electric power necessary for the twostandards of the recordable/rewritable compact disc (CD-R/RW) and therecordable/rewritable digital versatile disc (DVD-R/RW). When speed atwhich data is to be recorded in the CD-R/RW is assumed to be 16 times ashigh as the normal speed, power (electric power) required by the laserdiode LD becomes 160 mW expressed in the form of laser diode radiationelectric power, and electric power required by the laser diode LD torecord data in the DVD-R/RW becomes 70 mW expressed in the form of laserdiode radiation electric power. Having compared two center values of theabove-mentioned laser diode radiation electric power, it is to beunderstood that they have already differed from each other more thantwice.

Further, having considered dispersion of individual laser diodes LD inaddition to the difference of the laser diode radiation electric power,a range greater than ±12 dB is required as the range in which aparameter of a circuit is to be adjusted. Therefore, when it is intendedto secure such a wide range for adjusting a parameter of a circuit froma circuit design standpoint, it becomes impossible to maintain theperformance of the laser diode LD, such as the offset.

In order to realize the laser diode drive apparatus capable of readingand writing both the above-mentioned CD-R/RW and the above-mentioned.DVD-R/RW, as shown in FIG. 1, there are required two high-output laserdiodes LD1 and LD2 generating laser beams having wavelengths of 650 nmand 780 nm respectively. It is possible to realize functions necessaryfor the laser diode drive apparatus, even when an operational amplifieris configured in such a manner that the LD1 and LD2 are in separateoptical systems. However, in this case it becomes unavoidable that thelaser diode drive apparatus becomes large in size and becomes veryexpensive.

Accordingly, a demand for an operational amplifier having as manycomponents other than the laser diode LD in common as possible isincreasing.

FIG. 1 of the accompanying drawings is a schematic circuit diagram inblock form, which shows a laser diode drive circuit for use in anoptical disc recording and/or reproducing apparatus according to therelated art. As shown in FIG. 1, this related-art laser diode drivecircuit is comprised of a laser diode drive circuit, a power monitorcircuit and an automatic power control (APC) circuit, whereby the twolaser diodes LD1 and LD2 generating the laser beams having thewavelengths of 650 nm and 780 nm can be controlled respectively.

As shown in FIG. 1, this APC circuit has a configuration of usingelements and parts in common in the circuit necessary for the two laserdiodes LD1 and LD2, and only electric power is switched over to be set.Similarly, a laser diode drive power supply circuit LDD can be providedwith two output terminals used to switch-over an output and otherportion (power monitor circuit) of the laser diode drive circuit can beused in common.

The power monitor circuit for the disc writing laser diodes LD1 and LD2is adapted to receive and monitor several percents (this numerical valuechanges depending upon design of the optical system) of emitted power oflaser beams from the laser diode LD1 or LD2 by a monitor diode PD. Inthat case, when the power monitor circuit includes only one laser diodeLD, a change in quantity of incident light due to a fluctuation of adivergent angle of the laser diode LD or a fluctuation of a beamsplitter is within a range of approximately ±6 dB. When the change inthe quantity of incident light falls within the above-mentioned range,it is possible to adjust the conversion resistance value of thecurrent-to-voltage converting circuit of the front monitor photodetector(FDP) circuit in response to dispersion of individual operationalamplifiers without sacrificing the performance such as an operationband, offset, or the like.

However, when electric power necessary for writing data in two standardsof the CD-R/RW and the DVD-R/RW is considered, power (electric power)required by the laser diode LD necessary for the CD-R/RW becomes 160 mWand power required by the laser diode LD in the DVD-R/RW becomes 70 mWexpressed in the form of laser diode radiation electric power at drivespeed of the CD-R/RW being 16 times as high as the normal speed.Accordingly, two center values of the above-mentioned laser dioderadiation electric power have already differed from each other more thantwice. Further, having considered dispersion of individual laser diodesLD in addition to the fluctuations of the laser diode radiation electricpower, a range greater than ±12 dB is required as the range in which aparameter of a circuit is to be adjusted. Thus, it becomes difficult tomaintain the performance of the laser diode LD, such as the offsetsatisfactorily.

Furthermore, if the dynamic range of the optical disc recording and/orreproducing apparatus is doubly changed with respect to the CD-R/RW orthe DVD-R/RW, then the available power margin is narrowed unavoidably.As a result, setting accuracy on the DVD-R/RW side where power should beset with high accuracy is doubly degraded, which is not preferable.

SUMMARY OF THE INVENTION

In view of the aforesaid aspect, it is an object of the presentinvention to provide a laser diode drive circuit for use in an opticaldisc recording and/or reproducing apparatus in which optimal conversionsensitivities for respective circuits can be maintained withoutsacrificing operation characteristics of the respective circuits.

It is another object of the present invention to provide an amplifyingcircuit for use with such a laser diode drive circuit of an optical discrecording and/or reproducing apparatus.

According to an aspect of the present invention, there is provided alaser diode drive circuit for an optical disc recording and/orreproducing apparatus which is comprised of a plurality of laser diodesoutputting laser beams having different wavelengths, a switch circuitfor selectively connecting a required laser diode from the plurality oflaser diodes, a laser diode drive power supply circuit for driving thelaser diode selectively connected by the switch circuit, a photodiodefor detecting at least part of laser beams emitted from the laser diodeand converting a detected part of laser beams into an electrical signal,a plurality of current-to-voltage conversion amplifiers connected to anoutput of the photodiode, being capable of adjusting conversionresistance values and having differently designed center conversionresistance values and an automatic power control circuit connected tooutputs of the current-to-voltage conversion amplifiers to output afeedback signal to the laser diode drive power supply circuit.

According to other aspect of the present invention, there is provided anamplifying circuit comprised of a plurality of current-to-voltageconversion amplifiers connected in parallel being capable of adjustingconversion resistance values and having differently designed centerconversion resistance values, and a change-over switch provided at aninput side and output side of each current-to-voltage conversionamplifier, wherein one amplifier is selectively connected underswitch-over control of the change-over switches.

According to a further aspect of the present invention, there isprovided an optical disc recording and/or reproducing apparatusincluding a laser diode drive circuit. This laser diode drive circuit iscomprised of a plurality of laser diodes for outputting laser beamshaving different wavelengths, a switch circuit for selectivelyconnecting a required laser diode from a plurality of laser diodes, alaser diode drive power supply circuit for driving the laser diodeselectively connected by the switch circuit, a photodiode for detectingat least part of laser beams emitted from the laser diode and convertinga detected part of laser beams into an electrical signal, a plurality ofcurrent-to-voltage conversion amplifiers connected to an output of thephotodiode, being capable of adjusting conversion resistance values andhaving differently designed center conversion resistance values, and anautomatic power control circuit connected to outputs of thecurrent-to-voltage conversion amplifiers to output a feedback signal tothe laser diode drive power supply circuit.

In accordance with yet a further aspect of the present invention, thereis provided a laser diode drive method for an optical disc recordingand/or reproducing apparatus, comprising the steps of: selectivelyconnecting a required laser diode from a plurality of laser diodeshaving different output wavelengths to a laser diode drive power supplycircuit with a first switch circuit, driving the laser diode drive powersupply circuit to allow the connected laser diode to emit laser beams,detecting at least part of laser beams emitted from the laser diode toconvert the detected part of laser beams into an electrical signal by aphotodiode, outputting the electrical signal to a correspondingcurrent-to-voltage conversion amplifier of a plurality ofcurrent-to-voltage conversion amplifiers, being capable of adjustingconversion resistance values and having differently designed centerconversion resistance values, wherein the electrical signal iscurrent-to-voltage-converted and is amplified, selectively connecting anoutput of a required current-to-voltage conversion amplifier from theplurality of current-to-voltage conversion amplifiers to an automaticpower control circuit with a second switch circuit, generating afeedback signal by the automatic power control circuit from theelectrical signal which is current-to-voltage-converted and wasamplified and outputting the feedback signal to the laser diode drivepower supply circuit to effect a closed loop control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a circuit arrangement of a laser diodedrive apparatus for use in an optical disc recording and/or reproducingapparatus according to the related art;

FIG. 2 is a block diagram showing an example of an optical discrecording and/or reproducing (write and/or read) apparatus according tothe present invention;

FIG. 3 is a block diagram showing a circuit arrangement of a laser diodedrive apparatus for use in an optical disc recording and/or reproducingapparatus according to an embodiment of the present invention; and

FIG. 4 is a block diagram showing a circuit arrangement of a laser diodedrive apparatus for use in an optical disc recording and/or reproducingapparatus according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A laser diode drive circuit and an amplifying circuit for use in anoptical disc recording and/or reproducing apparatus according to thepresent invention will be described below with reference to thedrawings.

FIG. 2 is a block diagram showing an example of an optical discrecording and/or reproducing (write and/or read) apparatus according tothe present invention. According to this optical disc recording and/orreproducing apparatus, information may be recorded on the optical discand/or reproduced from the optical disc, as briefly described below withreference to FIG. 2.

As shown in FIG. 2, when information is recorded on the optical disc inthis optical disc recording and/or reproducing apparatus, a controlsignal and write data transmitted from an interface are supplied to anencoder. Data encoded by the encoder is supplied to an APC circuit to becontrolled in power. Then, the data processed by the APC circuit issupplied to an optical pickup (OP), in which the processed data isoptically modulated and is then properly focused on a rotating opticaldisc, thereby being recorded on the optical disc.

Also, when information is reproduced from the optical disc in thisoptical disc recording and/or reproducing apparatus, informationrecorded on the optical disc is reflected in the reflected light thathas been irradiated on the optical disc by a laser diode (LD). Thisreflected light is supplied to a photodetector (PDIC) whichphotoelectrically converts the reflected light to provide an RF signal.This RF signal is supplied to a signal processing circuit to extract aservo signal and a read data signal. The read data signal is supplied toa decoder to be decoded and the decoded read data signal is transmittedto the outside through an interface under control of a controller.

In this optical disc recording and/or reproducing apparatus, the laserdiode (LD) in the optical pickup (OP) is switched-over depending uponthe type of optical disc, and light emitted from the working laser diode(LD) is irradiated on the optical disc through a combined prism.

Part of light emitted from the laser diode (LD) is fed through asemiconductor chip (FPD-IC) of a front monitor photodiode (FPD) back tothe APC circuit, where it is used for a variety of control operations.These control operations will be described below in association with alaser diode drive circuit (LDD) with reference to FIG. 3 in which casethe FPD-IC (shown in FIG. 2) is represented as a photodetector PD(photodetectors PD1, PD2).

FIG. 3 is a block diagram showing a laser diode drive circuit for use inan optical disc recording and/or reproducing (write and/or read)apparatus according to an embodiment of the present invention.

As shown in FIG. 3, there are provided laser diodes LD1 and LD2 adaptedto generate laser beams for recording and/or reproducing. These laserdiodes LD1 and LD2 are driven by power supplied from a laser diode drivepower source circuit LDD. An output from this laser diode drive circuitLDD is switched over by a switch SW3 and supplied to either the laserdiode LD1 or LD2.

Let it now be assumed that the switch SW3 is connected to the contactillustrated in FIG. 3. The laser diode LD1 is being driven and data isbeing written in the disc with laser beams emitted from the laser diode.Then, part of the emitted laser beams is received by a photodiode PD andthat is introduced into an operational amplifier A1 through the contactof a switch SW1 illustrated in FIG. 3, where an output current of thephotodiode PD is converted into a voltage. An output from theoperational amplifier A1 is supplied through the illustrated contact ofa switch SW2 to an inverting input terminal of a comparing operationalamplifier A3 in an APC (auto power control) circuit.

A reference voltage source REF is connected to a non-inverting inputterminal of the comparing operational amplifier A3, and the comparingoperational amplifier A3 compares the signal supplied to the invertinginput terminal with the reference voltage supplied to the non-invertinginput terminal. A detected error signal is supplied from the outputterminal of the comparing operational amplifier A3 to the laser diodedrive power supply circuit LDD. Although there is illustrated only onereference voltage source REF in FIG. 3, in actual practice, there areprovided different reference voltage values the number of whichcorresponds to the number of power levels of laser beams.

Part of laser beams emitted from the laser diodes LD1, LD2 is obtainedby a suitable means and led to the above-mentioned detection photodiodePD. However this process is not directly related to the presentinvention and therefore need not be described in detail.

The laser diode LD1 is controlled by a signal received at the photodiodePD and then supplied through the switch SW1, the amplifier A1, theswitch SW2 and the comparing operational amplifier A3 back to the laserdiode drive power supply circuit LDD in such a manner that the laserdiode drive power supply circuit LDD may be driven at constant outputpower. Specifically, if it is determined that there is no error signalby comparing the voltage of the feedback signal and the referencevoltage in the comparing operational amplifier A3, the output of thelaser diode drive power supply circuit LDD is not changed at all.

As intensity of light emitted from the laser diode LD1 increases, theintensity of the signal detected by the photodiode PD also increases sothat the intensity of the signal fed back to the comparing operationalamplifier A3 also increases. Therefore, a negative feedback signal issupplied from the comparing operational amplifier A3 to the laser diodedrive power supply circuit LDD in order to decrease intensity of theoutput of the laser diode LD1 by the laser diode drive power supplycircuit LDD. Also, when intensity of light emitted from the laser diodeLD1 decreases, intensity of the output from the laser diode LD1 isincreased by the laser diode drive power supply circuit LDD.

While the case where the laser diode LD1 is controlled has beendescribed so far, the present invention is not limited thereto and thelaser diode LD2 can be controlled similarly as described above.Specifically, the contact positions of the switches SW1, SW2 and SW3 maybe changed-over to the opposite sides and control operations similar tothose of the above-mentioned case may be carried out.

Although only one APC circuit is illustrated in the circuit arrangementin FIG. 3 in order to make the present invention clearly understandable,in actual practice, there are provided a plurality of APC circuits, thenumber of which corresponds to the number of power levels of laserbeams. These APC circuits are connected in parallel, and upon use, arequired APC circuit is connected to the drive circuit.

Although output voltages of the current-to-voltage conversion amplifiersA1, A2 connected to the output of the photodiode PD can be adjusted byvariable resistors R1, R2, the ranges adjusted by these variableresistors R1, R2 are limited.

When the laser diodes LD1, LD2 and other circuit elements are used anddriven by change-over switches, the operation range is unavoidablywidened, and hence it becomes difficult for only one amplifier tocontrol all the driving of these circuit elements. Moreover, when oneamplifier is used in common for all the driving of these circuitelements, the operation characteristics of the current-to-voltageconversion amplifier cannot be maintained satisfactorily.

In order to solve the above-mentioned problem, in the laser diode drivecircuit according to an embodiment of the present invention as shown inFIG. 3, there are prepared a plurality of current-to-voltage conversionamplifiers. When a laser diode having a different wavelength is in use,a proper amplifier can be selected from a plurality of amplifiersprepared as described above and then used, which will be described belowmore in detail.

In the circuit shown in FIG. 3, during the period in which the laserdiode LD1 is being operated, the output of the photodiode PD isconnected to the contact of the amplifier A1 side by the switch SW1 andthen the output voltage of the amplifier A1 is inputted to the APCcircuit through the switch SW2, in which the voltage is compared withthe reference voltage REF and a difference voltage is fed back to thelaser diode drive power supply circuit LDD.

On the other hand, when the laser diode LD2 is being operated, theoutput of the photodiode PD is connected to the contact of the amplifierA2 side by the switch SW1 and then the output voltage of the amplifierA2 is inputted through the switch SW2 to the APC circuit, in which thevoltage is compared with the reference voltage REF and a differencevoltage is fed back to the laser diode drive power supply circuit LDD.

In the circuit shown in FIG. 3, if the current-to-voltage conversionamplifiers A1, A2 and the switches SW1, SW2 are fabricated as onecircuit which is connected to the laser diode drive circuit as required,the design of the circuit can be made easy.

While the laser diode drive circuit that has been described so far withreference to FIG. 3 uses only one power monitor photodiode PD, thepresent invention is not limited thereto, and the following variant isalso possible. That is, in the second embodiment of the presentinvention shown in FIG. 4, the above-mentioned power monitor photodiodeis comprised of a plurality of photodiodes PD1, PD2. Current-to-voltageconversion amplifiers A1, A2 are connected to the outputs of therespective photodiodes PD1, PD2 and are selectively connected to theabove-mentioned automatic power control (APC) circuit by the switchcircuit SW2. In FIG. 4, elements and part identical to those of FIG. 3are denoted by identical reference numerals and therefore need not bedescribed.

According to the laser diode drive circuit for the optical discrecording and/or reproducing apparatus of the present invention, sincethere are provided a plurality of adjustable operational amplifiers,wherein an optimum operational amplifier is inserted into the circuit byoperating switches, there can be carried out the optimumcurrent-to-voltage (1/V) conversion sensitivity adjustment with respectto the respective laser diodes LD comprising the light source.

Further, according to the laser diode drive circuit for the optical discrecording and/or reproducing apparatus of the present invention, sincethere are prepared a plurality of current-to-voltage conversionamplifiers having different operation characteristics, the dynamic rangeof the circuit can be used efficiently by selecting a requiredcurrent-to-voltage conversion amplifier by the change-over switches.

Furthermore, according to the laser diode drive circuit for the opticaldisc recording and/or reproducing apparatus of the present invention,since there are prepared a plurality of current-to-voltage conversionamplifiers having different operation characteristics and which can bechanged-over by the switches upon use, the operation band, the offsetand the noise characteristic can be adjusted excellently for each laserdiode LD.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

1. A laser drive circuit comprising: a plurality of laser diodesconfigured to output light having different wavelengths; a switchconfigured to selectively connect a predetermined laser diode from saidplurality of laser diodes to a laser diode drive supply circuit; aphotodiode configured to detect light emitted from said predeterminedlaser diode and output an electrical signal based on said detection; aplurality of amplifiers, at least one of said plurality of amplifiersoperably linked to an output of said photodiode; and an automatic powercontrol circuit operably linked to outputs of at least two of saidplurality of amplifiers and configured to output a feedback signal tosaid laser diode drive power supply circuit.
 2. The laser drive circuitaccording to claim 1, wherein said automatic power control circuit isoperably linked to an output of one of said plurality of amplifiers viaanother switch.
 3. The laser drive circuit according to claim 1, whereinsaid plurality of laser diodes is configured to output light atdifferent levels.
 4. The laser drive circuit according to claim 1,wherein at least one of said plurality of amplifiers is configured toadjust resistance values.
 5. The laser drive circuit according to claim4, wherein said resistance values correspond to different power outputlevels of said plurality of laser diodes.
 6. The laser drive circuitaccording to claim 1, wherein said photodiode comprises a plurality ofdiodes and each output of said plurality of diodes is respectivelyconnected to an input of one of said plurality of amplifiers, and aplurality of switch circuits are provided between outputs of saidplurality of amplifiers and an input of said automatic power controlcircuit.
 7. An optical pickup, comprising: a plurality of laser diodesconfigured to output light having different wavelengths; a switchconfigured to selectively connect a predetermined laser diode from saidplurality of laser diodes to a laser diode drive supply circuit; aphotodiode configured to detect light emitted from said predeterminedlaser diode and output an electrical signal based on said detection; aplurality of amplifiers operably linked in parallel and configured toadjust resistance values corresponding to respective different poweroutput levels of said plurality of laser diodes; and a plurality ofchange-over switches provided at the input sides and output sides ofsaid plurality of amplifiers, whereby one of said plurality ofamplifiers operably linked in parallel is selectively connected underchange-over control of said plurality of change-over switches.
 8. Anoptical disc recording and/or reproducing apparatus, comprising: aplurality of laser diodes configured to output light having differentwavelengths; a switch circuit for selectively connecting a predeterminedlaser diode from said plurality of laser diodes to a laser diode drivepower supply circuit; a photodiode configured to detect light emittedfrom said laser diode and convert the detected light into an electricalsignal; a plurality of amplifiers, at least one of said plurality ofamplifiers operably linked to an output of said photodiode; and anautomatic power control circuit operably linked to outputs of saidplurality of amplifiers to output a feedback signal to said laser diodedrive power supply circuit.
 9. The optical disc apparatus according toclaim 8, wherein said automatic power control circuit is operably linkedto an output of one of said plurality of amplifiers via another switch.10. The optical disc apparatus according to claim 8, wherein saidplurality of laser diodes is configured to output light at differentlevels.
 11. The optical disc apparatus according to claim 8, whereinsaid plurality of amplifiers is configured to adjust resistance values.12. The optical disc apparatus according to claim 11, wherein saidresistance values correspond to different power output levels of saidplurality of laser diodes.
 13. A method of driving a plurality of laserdiodes in an optical disc apparatus, comprising: selectively connectinga laser diode of a plurality of laser diodes having different outputwavelengths to a laser diode drive power supply circuit; driving saidlaser diode drive power supply circuit to allow the operably linkedlaser diode to emit light; detecting light emitted from said laser diodeand converting said detected light into an electrical signal; providingsaid electrical signal to one of a plurality of amplifiers; selectivelyconnecting an output of said one of said plurality of amplifiers to anautomatic power control circuit; generating a feedback signal at theautomatic power control circuit from said electrical signal; andproviding said feedback signal from the automatic power control circuitto said laser diode drive power supply circuit.
 14. The method of claim13 wherein said step of generating a feedback signal further comprises:adjusting resistance values of at least two of said plurality ofamplifiers.
 15. The method of claim 14, wherein said step of adjustingresistance conversion values further comprises: correspondinglyadjusting at least two resistance values in accordance with differentpower output levels of said plurality of laser diodes.
 16. A laser drivecircuit comprising: means for emitting light of different wavelengths;means for connecting said means for emitting to a means for driving saidmeans for emitting; means for detecting light emitted from said meansfor emitting, said means for detecting outputting an electrical signalbased on said detection; a plurality of means for convertingcurrent-to-voltage, each of said plurality of said means for convertingincluding means for receiving said electrical signal based on detection;means for selecting one of said plurality of means for convertingcurrent-to-voltage; and means for controlling power operably linked tooutputs of said means for converting, said means for controlling poweroutputting a feedback signal to said means for driving.
 17. The laserdrive circuit according to claim 16, wherein said means for selectingincludes at least one switch.
 18. The laser drive circuit according toclaim 16, wherein said means for emitting includes a plurality of laserdiodes confignred to output light at different levels.
 19. The laserdrive circuit according to claim 16, wherein said means for convertingis configured to adjust resistance values.
 20. The laser drive circuitaccording to claim 19, wherein said resistance values correspond todifferent power output levels of said means for emitting.
 21. The laserdrive circuit according to claim 16, wherein said means for detectingcomprises a plurality of diodes and outputs of said plurality of diodesare each respectively connected to an input of one of said plurality ofmeans for converting.